It is illegal for an employer to use age as a factor in hiring, terms and conditions of employment, in promotion, demotion, discipline, failure to accommodate, termination, etc. Under state law (New York and New Jersey), age discrimination is prohibited against any person over the age of 18. Under federal law, the age is 40 and over. State laws often are more generous than federal law in age discrimination cases.
Age discrimination is often difficult to prove. Often times there is no age-based comments (such as “you’re too old” or “are you retiring soon?”), and there is often no paper trail of proof. However, if there is no direct proof of age discrimination, the employee could provide indirect proof of discriminatory adverse employment action. See Article on Indirect Proof of Discrimination